Attck of teh AzN Cow flu! (cowbert) wrote in freebsd_users,
Attck of teh AzN Cow flu!

Hyperthreading dmesg

Dear Lazyweb -

Does disabling hyperthreading in BIOS cause <HTT> to disappear from CPU features in dmesg.boot? Or does it only affect "Logical CPUs per core:"?

Also, does the "Logical CPUs per core:" message require booting an SMP-aware kernel? (Since the multiproc enumeration only takes place after these messages and the ACPI APIC table brand echo).

This is on 6.3
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I think HTT remains, since it's just decoding the result of the CPUID instruction.

Yes, HTT / logical CPUs requires SMP, since aside from some instruction scheduling issues it's implemented precisely the same way at the OS level. (Note that "instruction scheduling issues" means that, unless applications are HTT-aware, running SMP/HTT can be considerably slower than UP because some instructions can't be run in parallel and will be forced to serialize by the CPU.)
ok I will boot an SMP kernel on this and see if it picks up more than 1 logical cpu (since I have no console access - it's in a colo facilty, I can't tell if HTT is enabled on this machine).